Patent Literature 1 describes “being provided with a master cylinder that generates a fluid pressure corresponding to a brake operational force of a driver, wheel cylinders using at least the master cylinder as their fluid pressure source to generate braking force in respective wheels, a fluid pressure source that is different from the master cylinder and is capable of supplying fluid pressure to the wheel cylinders, fluid pressure control means capable of arbitrarily controlling wheel cylinder pressure, a plurality of fluid pressure oil supply paths connecting the fluid pressure source and the respective cylinders, and a connection oil path connecting the fluid pressure oil supply paths to each other and including a normally-closed shutoff valve, where the fluid pressure control means executes brake-by-wire control of supplying braking fluid pressure to the wheel cylinders by the fluid pressure source being driven according to the braking operation by the driver”.
Specifically, electromagnetic valves are brought to open positions in a case where a master cylinder pressure changing rate is less than −ΔPo, and the fluid pressure of the wheel cylinders is reduced by a pump being driven in reverse. In a case where “the master cylinder pressure changing rate is greater than “0” but smaller than ΔPo (step 107)” is affirmed, the pump is stopped, and the electromagnetic valves are brought to closed positions to retain the fluid pressure in the wheel cylinders. Moreover, in a case where “the master cylinder pressure changing rate is greater than “0” but smaller than ΔPo” is denied, an isolation valve and the electromagnetic valves are brought to the open positions to rotate the pump forward, and the fluid pressure of the wheel cylinders are thereby increased. Due to this, the fluid pressure supplied to the wheel cylinders become even on right and left sides despite a presence of variations in pressure generated by gear pumps, and it is described that stable braking is thereby ensured.
In a braking control device described in Patent Literature 1, the isolation valve (connection valve) is normally in the open position in the case where the fluid pressure of the wheel cylinders is increased by control. However, since there are cases where the fluid pressure is independently controlled for each wheel, such as in a case of addressing pipe failures in a brake system and in a vehicle stabilization control (ESC), it is preferable to set the connection valve normally to the closed position (that is, a normally-closed electromagnetic valve is preferably employed). Further, in the case where the normally-closed connection valve is employed, power is needed to bring it to the open position, so from the viewpoint of energy consumption saving, it is desirable that this valve is controlled to the open position only in cases where needed.